In an extra-corporeal blood treatment process, such as a hemodialysis for example, the blood to be treated flows, in an extra-corporeal blood circuit, through the blood chamber of a dialyser which is divided by a semi-permeable membrane into the blood chamber and a dialysis-fluid chamber, while dialysis fluid flows, in a dialysis-fluid system, through the dialysis-fluid chamber of the dialyser. The extra-corporeal blood circuit has an arterial flexible tubing line which runs to the blood chamber and a venous flexible tubing line which leads away from the blood chamber. The flexible tubing lines of the extra-corporeal blood-treating apparatus are generally provided in the form of disposable items intended to be used only once. The known pieces of blood-treating apparatus have a blood pump, which is generally arranged upstream of the blood chamber of the dialyser, to ensure that there is an adequate flow of blood in the extra-corporeal blood circuit.
There are stringent technical requirements which the blood pumps have to meet. There are therefore only certain types of pump which can be considered. What have proved successful in practice are flexible tube pumps which pump the patient's blood through the arterial and venous flexible tubing lines.
The flexible tube pumps are also referred to as peristaltic pumps from the way in which they operate. Their pumping action is based on the fact of at least one point of constriction or closure (an occlusion) moving along the elastic flexible tubing line which acts as a pumping chamber and thereby displacing the trapped liquid in the direction of pumping.
In the most widely used type of flexible tube pump, the setting is such that the elastic flexible tubing is completely closed off at the moving constrictions. These pumps are therefore also referred to as occlusive flexible tube pumps.
The movable constrictions or occlusions which carry the blood along in the flexible tubing in the pump may take different forms. Roller pumps are known in which the flexible tubing is inserted between a stator, which forms a curved roller track acting as an abutment, and a rotor which is mounted to be rotatable within the track and which is fitted with rollers, which means that the rollers roll over the flexible tubing in the direction of pumping. The rollers are preferably spring-mounted on the rotor so that they exert an applied compressive force on the flexible tubing. As well as the above, what are also known are finger pumps in which the occluding bodies are formed by a series of movable compressing members (fingers) arranged along the flexible tubing.
An overview of the different types of roller and finger pump is given in Dialysetechnik, 4th edition, Gesellschaft für angewandte Medizintechnik m.b.H. and Co. KG, Friedrichsdorf, 1988.
The requirements which exist for flexible tube pumps of this kind to operate properly in pieces of medical apparatus, and particularly in pieces of blood-treating apparatus, are demanding ones. In the known pieces of blood-treating apparatus, peristaltic flexible tube pumps are used not only to pump the blood but also to pump other liquids.
During the operation of the peristaltic flexible tube pump, there is a danger that the flexible tubing line inserted in the flexible tube pump may not be properly positioned in the bed of the pump or that the displacing bodies may not be guided properly over the flexible tubing line. If the peristaltic flexible tube pump has a fault of this kind, there is no guarantee that the pump will operate properly. If the segment of flexible tubing is not correctly positioned in the bed of the pump, there is a particular risk of the flexible tubing line being damaged. If nothing else, because of the possibility of the flexible tubing line not being adequately occluded there is no guarantee of the liquid being pumped properly.
U.S. Pat. No. 5,629,871 describes a method and an arrangement for monitoring the ability to operate of various sub-assemblies of a hemodialysis apparatus. These include the flexible tube pumps, with the current or the supply voltage to the flexible tube pumps being monitored to enable any failure of the pumps to be detected.
It is known from U.S. Pat. No. 4,781,525 for the current to a pump to be used to determine the pumping rate. WO 97/45150 describes a method of determining the pumping pressure of a pump in which the current to the pump is determined.
Known from WO 2007/104435 A2 is a method and an arrangement for operating an electric peristaltic flexible tube pump and in particular a flexible tube pump for pumping liquids in pieces of extra-corporeal blood-treating apparatus. To allow the proper operation of the flexible tube pump to be monitored, the power consumption of the pump, or a physical variable which correlates with its power consumption, is monitored. The monitoring of the current to the pump is based on the fact that the current to it has a D.C. component which does not vary cyclically and on which an A.C. component which does vary cyclically is superimposed. To allow the proper operation of the flexible tube pump to be monitored, the way in which the A.C. component of the power consumption rises and falls in relation to the D.C. component of the power consumption is monitored during the blood treatment.